Pre-manufactured cast concrete blocks of various designs have been used in the construction industry for many years. One commonly employed concrete block design is often referred to as a CMU (Concrete Masonry Unit). Typically, a bed of mortar is manually applied over the blocks, which are then hand set and aligned into the mortar in a staggered fashion to create mortar joints therebetween. The construction is therefore highly labor intensive. The CMU is sized to balance ease in handling and the ability to construct walls of various shapes, with being large enough to reduce the total number of manual operations required in constructing those walls. While the size of a CMU varies internationally, the most common nominal size is 16 inches×8 inches×8 inches (about 410 mm×200 mm×200 mm).
Because concrete is strong in compression, but relatively weak in tension, concrete is often structurally reinforced to compensate for this structural imbalance. Thus, CMUs are typically made with hollow channels, sometimes referred to as voids or cores, that permit the deployment of steel rebar (reinforcement bar) there through. Because the blocks are staggered, the channels or voids overlap from one layer to another, permitting rebar to extend from the top of the wall to the bottom. The rebar is typically secured within the voids using grout or concrete.
While this technique of reinforcement can be effective to internally reinforce a constructed wall, the reinforcement process, when combined with the process of actually laying the blocks is highly labor intensive, time consuming, and therefore costly. Furthermore, variations in environmental conditions as well as the skill of the masons during construction, can lead to inconsistencies in the quality of a completed wall.
In an attempt to lower the cost of construction, the construction industry has also employed building blocks that are much larger in size than the CMU. However, as the size of concrete blocks increase, they have tendency to become brittle, thereby necessitating reinforcement. To further reduce construction costs, the larger prefabricated blocks are sometimes pre-fabricated with internal reinforcement materials already built into the block during fabrication. Not only does this render the pre-reinforced blocks more difficult to handle and transport, but the reinforcement materials are neither interconnected, nor are they directly coupled to external structures used to create overall stability of the walls. This lack of integration can result in overuse of such reinforcement material to achieve a wall of a desired strength.
It should be further pointed out that while the geometry of CMUs and other concrete blocks is favorable for providing reinforcement in vertical and horizontal planes, walls constructed of such blocks still tend to have low resistance to sheer stress, which makes them less than ideal for seismically-resistant construction.